Conventional pressure-sensitive adhesives for use in tape-shaped insulating materials include acrylic or rubber-based solvent type pressure-sensitive adhesives, which have good insulating characteristics. Similarly to general pressure-sensitive adhesives, however, such pressure-sensitive adhesives for use in tape-shaped insulating materials can also be a subject of public demands or a subject of enhancement of regulations concerning environmental protection, resource saving, safety and sanitation, or the like, and therefore development of solvent-free materials has been an important task. Thus, there has been a demand for alternatives to the solvent type pressure-sensitive adhesives. As the alternative to the solvent type pressure-sensitive adhesives, water-based pressure-sensitive adhesives can be superior to hot-melt or curing type pressure-sensitive adhesives in terms of general versatility and potential applications and developments.
However, the conventional water-based pressure-sensitive adhesive such as an aqueous dispersion type natural or synthetic rubber latex contains a very large amount of a water-soluble ionic emulsifying agent and therefore has a problem of degradation of insulating characteristics. On the other hand, there are some aqueous dispersion type acrylic pressure-sensitive adhesives, which contain a polymer emulsion produced by polymerizing a monomer mainly composed of an alkyl(meth)acrylate ester in the presence of an emulsifying agent. In the process of such a polymer, a functional group-containing monomer, which is co-polymerizable with the main component, or any other modifier monomer is added for the purpose of increasing the adhesive strength to the adherend, introducing crosslinking points for post-crosslinking of the resulting polymer, or enhancing the cohesion of the pressure-sensitive adhesive. However, the known aqueous dispersion type acrylic pressure-sensitive adhesives have the problem that their insulating characteristics can be degraded under humidified conditions.
It is an object of the invention to provide a tape-shaped insulating material comprising a water-based pressure-sensitive adhesive layer that is provided on one side or both sides of an insulating substrate and has good insulating characteristics. It is another object of the invention to provide an insulated product comprising the tape-shaped insulating material attached.
It is yet another object of the invention to provide a water-based pressure-sensitive adhesive layer having good insulating characteristics and to provide an aqueous dispersion type acrylic pressure-sensitive adhesive that is for use in insulating materials and can form a water-based pressure-sensitive adhesive layer having good insulating characteristics.